Mobile communication systems in recent years have developed rapidly. 3GPP (3rd Generation Partnership Project) is proceeding with standardization of LTE (Long Term Evolution) which realizes mobility complying with all types of traffic using an IP (Internet Protocol) protocol as a next mobile communication system. An LTE network is composed of eUTRAN (Evolved Universal Terrestrial Radio Network), which is a wireless network, and EPC (Evolved Packet Core), which forms a core network. Explained below is an allocation method of resources and load distribution method in an EPC network of a related art that have been also examined in, for example, “METHOD, SYSTEM AND DEVICE FOR SUPPORTING ADDRESSING THE USER STATIC IP ADDRESS IN LONG TERM EVOLUTION SYSTEM” disclosed in Published Japanese Translation of PCT International Publication for Patent Application, No. 2010-539758.
An MME (Mobility Management Entity) has a function to appropriately distribute loads and select an EPC node (MME/S-GW/P-GW/SGSN) taking into account a priority set to each of an NAPTR (Naming Authority Pointer) record/an SRV (Service) record that are registered to a DNS (Domain Name Server) server as DNS resource records and shown in Tables 1 and 2.
TABLE 1Format: NAPTR recordOrderPriority in a list of NAPTR RR returned at a time (smallervalues have higher priority)16 bit unsigned integerPreferenceRelative priority in records with the same value of Orderfield (smaller values have higher priority)16 bit unsigned integerFlagType of value in Replacement field Replacement“s” . . . Value in Replacement field is a key for SRV RRsearch“a” . . . Value in Replacement field is a key for A/AAAARR search“” . . . Value in Replacement field is a key for NAPTR RRsearchServiceService name, protocol name[Service name]:[Protocol name]:[Protocol name] . . .(:[Protocol name]) repeats 0 or more timesRegexpOutput resultReplacement rule using regular expressionReplacementOutput resultFQDN(Name of SRV RR & A/AAAA RR)
TABLE 2Format: SRV recordPriorityPriority in a list of SRV RR returned at a time (smaller valueshave higher priority)16 bit unsigned integerWeightRelative priority in records with the same value of Priority field16 bit unsigned integerPortConnection destination port number16 bit unsigned integer (0 to 65535)TargetConnection destination Registered to A/AAAA RRFQDN(Name of A/AAAA RR)
A flow of selecting an S-GW (Serving Gateway) to be connected by an MME (Mobility Management Entity) is explained using an explanatory diagram of FIG. 3. However, this not only applies to an S-GW but also to the case of selecting other types of EPC nodes that are an MME, an SGSN (Serving GPRS (General Packet Ratio Service) Support Node), and a P-GW (Packet data network Gateway). FIG. 3 is an explanatory diagram explaining a flow of processing for selecting an S-GW (Serving Gateway) by an MME (Mobility Management Entity) in an EPC (Evolved Packet Core) network of a related art. FIG. 3 shows the case in which there are three gateways that are an S-GW1 31, an S-GW2 32, and an S-GW3 33 as S-GWs to be selected.
In the explanatory diagram of FIG. 3, firstly an MME 35 queries a DNS server 34 for addresses of connectable S-GWs (Step S301). With the query, the MME 35 receives, from the DNS server 34, a plurality of NAPTR records shown in Table 1 indicating connectable S-GWs (Step S302). The MME 34, which received the plurality of NAPTR records, selects a particular NAPTR record with the highest priority according to priorities set to each of an Order field and a Preference field of the plurality of received NAPTR records.
Next, the MME 35 refers to a Flag field of the selected NAPTR record, and when Flag=“ ”, it indicates that an FQDN (Fully Qualified Domain Name) set to a Replacement field as an output result is set as a key for NAPTR RR (Resource Record) search. Thus, the MME 35 repeats an operation of querying the DNS server 34 again for an NAPTR record corresponding to the FQDN and an operation of receiving NAPTR records shown in Table 1 from the DNS server 34.
Moreover, when the Flag field of the selected NAPTR record upon reference by the MME 35 has setting of Flag=“a”, it indicates that an FQDN (Fully Qualified Domain Name) set to the Replacement field as an output result is a fully qualified domain name composed of an A/AAAA RR (an IPv4 address/an IPv6 address Resource Record) and the FQDN indicates an address of an S-GW to be selected. Thus, the MME 35 determines the S-GW as an S-GW to be selected.
Meanwhile, when the Flag field of the selected NAPTR record upon reference by the MME 35 has setting of Flag=“s”, it indicates that an FQDN (Fully Qualified Domain Name) set to the Replacement field as an output result is set as a key for SRV RR (Service Resource Record) search. Thus, the MME 35 queries the DNS server 34 for an SRV record corresponding to the FQDN and receives SRV records shown in Table 2 from the DNS server 34.
The MME 35, which received the SRV records from the DNS server 34, selects an SRV RR (Resource Record) with the highest priority according to priorities set to each of a Priority field and a Weight field of the received SRV records and retrieves an FQDN that is set to a Target field as a connection destination. When the FQDN indicates a fully qualified domain name of an A/AAAA RR (an IPv4 address/an IPv6 address resource record), the FQDN indicates an address of an S-GW to be selected. Thus, the MME 35 determines the S-GW as an S-GW to be selected.
Among the three gateways, which are the S-GW1 31, the S-GW2 32, and the S-GW3 33, the MME 35 transmits a connection command to a particular S-GW that is determined as the one to be selected according to the priority of the selected NAPTR record or the selected SRV record, for example to the S-GW2 32 (Step S303) to thereby connect to the corresponding S-GW, for example the S-GW2 32.
FIG. 4 is a sequence diagram showing a sequence of a control signal transmitted and received between the MME 35 and the DNS server 34 in the flow of processing in FIG. 3. Explained below is a flow of a control signal transmitted and received between the MME 35 and the DNS server 34 when the MME 35 selects an S-GW with reference to the sequence diagram of FIG. 4.
In the sequence diagram of FIG. 4, firstly the MME 35 transmits an NAPTR RR (an NAPTR resource record) query to the DNS server 34 and queries for addresses of connectable S-GWs (Sequence S401). The DNS server 34, which has received the NAPTR RR query from the MME 35, extracts a plurality of NAPTR RRs indicating connectable S-GWs and returns the extracted NAPTR RRs to the querying MME 35 as DNS responses to the NAPTR RR query (Sequence S402).
The MME 35, which received the DNS responses from the DNS server 34, selects one NAPTR RR according to a priority from an NAPTR RR list that is composed of a plurality of the received DNS responses. When the Flag field included in the NAPTR RR has setting of Flag=“s”, the MME 35 retrieves an FQDN, in the Replacement field, that indicates a domain name of an SRV RR (Sequence S403). After that, the MME 35 transmits an SRV RR (SRV resource record) query to the DNS server 34 and queries for the SRV record corresponding to the FQDN (Sequence S404).
The DNS server 34, which received the SRV RR query from the MME 35, appropriately extracts SRV RRs corresponding to the specified FQDN and returns the extracted SRV RRs to the querying MME 35 as DNS responses to the SRV RR query (Sequence S405).
The MME 35, which received the DNS responses from the DNS server 34, selects one SVR RR according to priorities from an SRV RR list of the received DNS responses (Sequence S406), transmits an A/AAAA RR query to the DNS server 34 when an FQDN (a Name of the A/AAAA RR) is set to the Target field as a domain name of the SVR RR, and queries for the A/AAAA RR (IPv4 address/IPv6 address resource record) of the SVR RR (Sequence S407).
The DNS server 34, which received the A/AAAA RR query from MME 35, extracts the fully qualified domain name A/AAAA RR corresponding to the specified SVR RR and returns the extracted A/AAAA RR to the querying MME 35 as a DNS response to the A/AAAA RR query (Sequence S408).